Postman not launching anymore in 18.04

I had the same problem on a clean 18.04 install, the library libgconf2-4 could not be found.

Try sudo apt install libgconf2-4, it should solve your problem.

Slight change to the answer provided by @Stanko worked for me.

Try adding hypen(-) in between libgconf and 2

sudo apt install libgconf-2-4